Angular momentum transfer and the size-mass relation in early-type galaxies

作者：Cardone V F^*; Del Popolo A; Kroupa P

来源：Monthly Notices of the Royal Astronomical Society, 2009, 400(2): 766-774.

DOI：10.1111/j.1365-2966.2009.15450.x

• galaxies: elliptical and lenticular
• Cd
• galaxies: fundamental parameters
• galaxies: kinematics and dynamics

Early-type galaxies (ETGs) define a narrow strip in the size-mass plane because of the observed correlation between the effective radius R(eff) and the total stellar mass M(star). When expressed in logarithmic units, a linear relation, log R(eff) proportional to gamma log M(star), is indeed observationally found, but the slope gamma deviates from the canonical gamma = 1/2 value which can be naively predicted for a spherically symmetric isotropic system. We propose here that a transfer of angular momentum to the stellar component induces an anisotropy in the velocity space, thus leading to a modified distribution DF). Assuming an Osipkov-Merritt like anisotropic DF, we derive an analytic relation between the slope gamma of the size-mass relation and the slope alpha of the angular momentum term in the DF. With this simple model, we are then able to recover the observed gamma value provided alpha is suitably set. It turns out that an anisotropy profile which is tangential inside similar to 0.6r(a) and radial outside, with r(a) the anisotropy radius, is able to reproduce the observed size-mass relation observed for massive (M(star) >= 2 x 1010 h-1 M(circle dot)) elliptical galaxies.

• 出版日期2009-12-1